Deterministic versus stochastic quantitative microbial Risk Assessment models for wastewater irrigation of food crops

Reuse of wastewater to irrigate food crops is being practiced in many parts of the world and is becoming more commonplace as the competition for, and stresses on, freshwater resources intensify. But there are risks associated with wastewater irrigation, including the possibility of transmission of pathogens causing infectious disease, to both workers in the field and to consumers buying and eating produce irrigated with wastewater. To manage these risks appropriately we need objective and quantitative estimates of them. This is typically achieved through one of two modelling approaches: deterministic or stochastic. Each parameter in a deterministic model is represented by a single value, whereas in stochastic models probability functions are used. Stochastic models are theoretically superior because they account for variability and uncertainty, but they are computationally demanding and not readily accessible to water resource and public health managers. We constructed models to estimate risk of enteric virus infection arising from the consumption of wastewater-irrigated horticultural crops (broccoli, cucumber and lettuce), and compared the resultant levels of risk between the deterministic and stochastic approaches. Several scenarios were tested for each crop, accounting for different concentrations of enteric viruses and different lengths of environmental exposure (i.e. the time between the last irrigation event and harvest, when the viruses are liable to decay or inactivation). In most situations modelled the two approaches yielded similar estimates of risk (within 1 order-of-magnitude). The two methods diverged most markedly, up to around 2 orders-of-magnitude, when there was large uncertainty associated with the estimate of virus concentration and the exposure period was short (1 day). Therefore, in some circumstances deterministic modelling may offer water resource managers a pragmatic alternative to stochastic modelling, but its usefulness as a surrogate will depend upon the level of uncertainty in the model parameters.

Experimental study of abattoir wastewater treatment from an economic perspective

The most cost effective treatment scheme for effluent from Midfield Meats, an abattoir in Warrnambool, Australia, was evaluated via a series of laboratory and commercial scale experiments. Effectiveness was measured in terms of suspended solids (SS) and biological oxygen demand (BOD) reduction. Economic assessment was based on predicted reduction in trade waste charges versus infrastructure and running costs. From the range of potential treatment technologies, those deemed most appropriate for trialling included pre-screening, sedimentation, coagulation and flocculation treatment and dissolved air floatation (DAF). Prior to evaluation of treatment types, flow, loads and contaminant characterisation of the waste streams was conducted to aid in selection of treatment type and capacity. Prescreening was found to be the most cost effective, followed by sedimentation, coagulation and flocculation treatment and finally DAF. The most economical treatment scheme that satisfied the requirements of Midfield Meats included a combination of prescreening and sedimentation. DAF and coagulation and flocculation treatment satisfactorily treated the wastewater, however were not cost effective under the current trade waste agreement.

In vitro and immunological assessment of the estrogenic activity and concentrations of 17β-estradiol, estrone, and ethinyl estradiol in treated effluent from 45 wastewater treatment plants in Victoria, Australia

The project was conducted between May 2006 and September 2007, and involved the collection of effluent samples from 45 wastewater treatment plants (WWTPs). The 45 WWTPs included 16 lagoon-based plants and 29 with activated sludge-based processes. Permission was obtained from all the relevant water authorities to collect samples of final effluent at point of discharge to the environment, whether that was to a creek, a river, the ocean, or the land. Samples were collected on two occasions, namely, in August 2006 (winter) and late February–early March 2007 (summer), and subjected to a number of biological and chemical analyses, including toxicity tests, measurement of hormonal (estrogenic) activity using yeast-based bioassays, and measurement of specific hormonal concentrations using enzyme-linked immunosorbent assays (ELISAs). Almost all of the effluents examined showed estrogenic activity: in winter, no activity to 73 ng/l 17β-estradiol equivalents (EEQ); and in summer, no activity to 20 ng/l EEQ. On the whole, the levels of estrogenic activity observed were comparable with the range recently reported in Australia and New Zealand using human estrogen receptor-based assays (“not detected” to ~10 ng/l EEQ). The low/no bioassay response was confirmed by the chemical assessment of estradiol, estrone, and ethinyl estradiol concentrations by ELISA, which returned concentrations of these compounds for the most part below 10 ng/l.

Aluminium smelter wastewater : groundwater fluoride fate

This study assessed the viability of utilising groundwater systems to manage Portland Aluminium's trade waste water stream. A mathematical groundwater model was created to assess laboratory and field results. Fluoride was modelled for spatio-temporal longevity in the system. All models indicate that fluoride will ultimately exit the site to the seaward boundary.

Integrated system for high quality water recovery and wastewater treatment

This thesis unveils an integrated system that once applied, could standardise and simplify the processes used for high quality water recovery and wastewater treatment. It forsees lower prices of desalinated and recovered water, in a streamlined and more efficient water industry, by departing from today's thinking of conventional wastewater treatment.

Simultaneous removal of ammonia and phosphate from wastewater by precipitation of struvite using magnesia

A thorough investigation of conditions required for the precipitation of magnesium ammonium phosphate hexahydrate using magnesia as the source of magnesium was carried out and two computer models were used to make predictions as to optimum conditions for production of suitable crystal size and structure for a successful process. A process was developed and a bench scale model operated for a number of high ammonia wastes. Removal of ammonia was affected to levels of up to 97% with 94% ammonia removal being achievable consistently.